The invention is directed to diaphragms which are self sustaining and flexible, and generally unstretchable once they are formed, with each diaphragm being formed to provide a peripheral flange by which the diaphragm is supported and held in place and an inner portion which is deflectable relative to the flange.
When opposite sides of a diaphragm are subjected to unequal pressures and flexed, stretching forces are applied radially and circumferentially. The two distinctly different types of stress are referred to as radial stress and circumferential stress (sometimes called "hoop stress"). The pressure differential also can cause shearing forces to occur at sharp angle intersections of portions of the surface, most notably at the transition between moveable and stationary portions of the diaphragm. With a sufficient pressure differential, developed forces can be focused to the central region of the diaphragm and result in "doming" if there is no means to limit deflection.
As one means of limiting deflection, a central member can be provided to offset the central loading forces such that a generally planar diaphragm will tend to deform permanently into an annular trough having its concavity on the high pressure side. For this reason, when forming a diaphragm having other than a planar surface, it is advantageous to preform and position the diaphragm so that major convexities are not on the high pressure side.
Heretofore, diaphragms have been formed with coaxial annular corrugations for the purpose of reducing or offsetting radial stresses from the deflection of the diaphragm. Also, in order to reduce or offset circumferential stresses and thus facilitate circumferential flexing of the diaphragm, radially disposed ribs or spokes have been added onto the annular corrugations.
With a generally non-planar, thin metal diaphragm having one or more annular corrugations, the metal of the corrugations tends to move radially towards the center of the diaphragm during deflection of the diaphragm toward the plane of the flange. This deflection of the diaphragm tends to reduce the diameter of a circular segment of metal particles so as to compress the metal of the segment into a smaller volume, with the resistance of the metal to such compression producing the "hoop stresses" and, ultimately, closing of the corrugation. On the other hand, the provision of radially directed corrugations or ridges allows for annular contraction and expansion so as to provide circumferential flexibility which counteracts "hoop stress".
Exemplary of a generally planar diaphragm having both annular and radial waveforms for stress relief are the devices of the above-referenced Zavoda patents. This prior art provides increased sensitivity over only a limited range of stroke distances and a limited central force loading capability and, since work is expressible as force times distance, it fails to accommodate any significant work.
Exemplary of a non-planar diaphragm being capable of accommodating central force loading is the device of the above-referenced Kelly patent which has a single annular trough and a plurality of radial corrugations. The radial corrugations inherently stiffen the trough and tend to limit sensitivity and stroke. Additionally, the angle of transition from the trough to a peripheral flange (and to a centrally disposed surface) of the diaphragm is sufficiently sharp as to restrict stroke distance. Thus, although able to accommodate rather significant central loading forces, the limiting of stroke distances restricts the amount of work capability.
The structure of the Kelly device also causes a concentration of forces at the relatively sharp "hinge" regions of transition between surfaces, most notably at the transition from the displaceable inner portion to the surrounding flange for retaining the diaphragm in a housing. An unexpectedly high pressure differential and/or repeated "hinging" of such diaphragms at lower pressure differentials leads to failures such as rupture or permanent deformation of the material at these "hinges".
It is an object of the invention to provide such a diaphragm with structural improvements over the prior art, specifically improvements in the shape and composition of the deflectable portion of the diaphragm.
Also, it is an object of the invention to minimize failures in those areas of a diaphragm which commonly have high failure rates from permanent deformation, by pressure differentials, of a convex surface configuration into that of a concave surface configuration (so called "blowout") and/or ruptures or the like, by the particular structure of the deflectable portion of the diaphragm and/or backing or limiting surfaces with which the deflectable portion contacts during use of the diaphragm.
Additionally, it is an object of the invention to prevent sharp "hinging" of such diaphragms in regions of transition between diaphragm surfaces of different cross-sectional contours, by means of physically modifying the areas of transition and/or providing backing surfaces which impose "smooth curve" behavior on the diaphragm material in these transition regions.
Further, it is an object of the invention to provide a diaphragm which is "sensitive" or easily deflects and recovers when subjected to slight pressure differentials, while also being capable of recovering after repeatedly deflecting further than prior art diaphragms which are proportionately similar in size.
Still further, it is an object of the invention to provide a diaphragm with an improved stroke distance and significant central force loading capability, resulting in significantly improved capacity to do work.
Another object of the invention is to provide such a diaphragm with a structure which provides improved "durability" for withstanding damage from extreme pressure differentials which are regularly and/or intermittently applied, whether or not they are anticipated.
These and other objects of the invention will become more apparent from the following disclosure, including the attached drawings.